The Ukrainian military said it again targeted oil refineries in the regions of Saratov and Samara, deep inside Russian territory.
Samara Governor Vyacheslav Fedorishchev said four people died and one person was injured in the attacks, the state-run TASS news agency reported.
He earlier said on social media that objects in the fuel and energy sector were the target of Ukrainian drone attacks, without specifying whether they were damaged.
According to the General Staff, the Ukrainian military attacked an oil refinery and other infrastructure in the region, as well as a facility in Saratov on the Volga River, which has been the target of several Ukrainian attacks including last week.
The governor of the Saratov region, Roman Busargin, wrote on Telegram that a woman was injured in Ukrainian drone attacks, and that windows in two apartment blocks and several cars were damaged.
He did not mention the refinery.
Russia launched a large-scale missile and drone attack targeting regions across Ukraine overnight, killing at least three people and wounding dozens more, Ukrainian officials said.
Ukrainian President Volodymyr Zelenskiy said attacks took place across nine regions including Dnipropetrovsk, Mykolaiv, Chernihiv, Zaporizhzhia, Poltava, Kyiv, Odesa, Sumy and Kharkiv.
"The enemy's target was our infrastructure, residential areas and civilian enterprises," he said, adding that a missile equipped with cluster munitions struck a multi-storey building in the city of Dnipro.
"Each such strike is not a military necessity but a deliberate strategy by Russia to intimidate civilians and destroy our infrastructure," he said in a social media post.
Zelenskiy said he expected to meet US President Donald Trump on the sidelines of the United Nations General Assembly next week.
He also said the first ladies of Ukraine and the United States would likely hold separate talks focused on humanitarian issues involving children.
Russia's Defence Ministry denied its aircraft violated Estonia's airspace after Estonian authorities reported three fighter jets crossed into its territory on Friday without permission and remained there for 12 minutes.
In a statement early on Saturday, Russia stressed its fighter jets had kept to neutral Baltic Sea waters more than 3km from Estonia's Vaindloo Island in the Gulf of Finland.
"On September 19, three MiG-31 fighter jets completed a scheduled flight from Karelia to an airfield in the Kaliningrad region," it said, referencing the Russian enclave sandwiched between Polish and Lithuanian territory.
"The flight was conducted in strict compliance with international airspace regulations and did not violate the borders of other states, as confirmed through objective monitoring," the statement said without providing details about the monitoring operation.
Estonian officials dismissed the denial, saying the violation was confirmed by radar and visual contact and suggested it could be a tactic to draw NATO resources away from Ukraine.
The Russian MIG-31 fighters entered Estonian airspace between 9.58am and 10.10am local time on Friday in the area of Vaindloo, a small island located in the Gulf of Finland in the Baltic Sea, the Estonian military said.
It still "needs to be confirmed," if the border violation was deliberate or not, Colonel Ants Kiviselg, the commander of Estonia's Military Intelligence Centre told the Associated Press.
Regardless, he said, the Russian jets "must have known that they are in (Estonian) airspace".
The Russian pilots didn't pose a "military threat," Kiviselg said.
with DPA
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